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Glossary
When too many respondents score at or near the minimum, the assessment can't distinguish between them or detect further decrease.
A floor effect occurs when too many respondents score at or near the minimum possible value on an assessment, so the test can't distinguish between them. A cognitive test designed for the general public might cluster respondents with advanced dementia all near zero — leaving the test unable to differentiate severity.
Floor effects matter for the same reasons as ceiling effects: they limit a test's ability to detect differences between respondents at one end of the range and to track change over time. The fix is usually a different instrument calibrated for that population.